1. Field of the Invention
The present invention relates to a method and an apparatus for slicing semiconductor wafers, and in particular, a method and an apparatus for slicing semiconductor wafers by a slicing machine with an inner peripheral cutting edge.
2. Description of the Related Art
In general, a columnar semiconductor material (hereafter, called a "workpiece") is sliced with a thin cutting edge to manufacture thin pieces like semiconductor wafers. An inner peripheral cutting edge of the doughnut-shaped blade in which diamond grains are electro deposited on the inner peripheral edge of the cutting edge. This inner peripheral cutting edge is stretched out at the outer peripheral side of the blade with a predetermined tension by the blade holding device to slice workpieces with high accuracy.
One conventional method for slicing semiconductor wafers with the inner peripheral cutting edge, as shown in FIG. 29, is a method in which the workpiece 1 moves in the direction of arrow B to be cut by the inner peripheral cutting edge 3 while the blade 2 is rotating in the direction of arrow A.
However, in this method for slicing, when an inside diameter of the blade 2 is D1 and an outside diameter is D2, it is necessary that a difference "(D2-D1)"(hereafter, called an "effective blade length") between inside and outside diameters of the blade 2 is larger than a diameter D of the workpiece 1.
The blade 2 is formed by press punching a thin rolled band- plate, and has no sense of direction externally for its circular shape. However, differences of tensile strength exist intrinsically in the radial direction and in the orthogonal direction. Consequently, when the diameter of the blade 2 becomes larger, the tension adjustment of the blade 2 becomes more difficult.
Therefore, the above-mentioned method has disadvantages in that the rigidity of the blade 4 is decreased to lower the processing accuracy of semiconductor wafers and the tension adjustment of the blade becomes extremely difficult when the inside and outside diameters of the blade 4 become larger as the diameter of the workpiece 1 is made bigger.
Another conventianal method shown in FIG. 30 has proposed as a method for slicing semiconductor wafers which solves such disadvantages. This method for slicing cuts the workpiece 1 while the workpiece 1 is rotated in the direction of arrow C and the blade 4 is rotated in the direction of arrow D and moves in the direction of arrow E.
According to this method, an effective blade length of the blade 4 can be reduced to 1/2 of the workpiece diameter since the workpiece 1 can be cut while the workpiece 1 is rotating. Therefore, it is possible to make the blade 4 smaller than the blade 2 shown in FIG. 29.
However, the conventional method for slicing semiconductor wafers shown in FIG. 30 has a disadvantage in that an apex projection (a cut remainder part) remains at the center of the cut semiconductor wafer.